The present invention relates to a hot air-blower, and more particularly to an off-state residual heat preventive control circuit for a hot air-blower, which keeps the fan motor operating for a certain length of time after turning off the main thermal resistor, enabling the temperature of the hot air-blower to be quickly lowered.
An industrial hot air-blower A, as shown in FIG. 1, is generally comprised of a high impedance thermal resistor B, and a fan motor C. When operated, the thermal resistor B produces heat as high as about 500xcx9c600xc2x0 C., and the fan motor C blows currents of air through the thermal resistor B toward the output port of the hot air-blower A. Because the hot air-blower A is hot during its operation, it must be carefully used. When turning off the hot air-blower A, electricity is cut from the thermal resistor B and the fan motor C, however the hot air-blower A is still very hot at this moment. One may be scalded severely when touching the surface of the hot air-blower A carelessly with the hand or a part of the body a short period of time after the hot air-blower A has been switched off. Because the industrial hot air-blower is normally left in place after an operation, it tends to be forced to fall down by an external object. If the industrial hot air-blower A falls from the standing position, its high temperature may burn or melt the surrounding objects. Furthermore, because the temperature of the hot air-blower A is not quickly reduced after each use, the winding of the fan motor and the related electronic component parts tend to be damaged by heat.
The present invention has been accomplished to provide a hot air-blower off-state residual heat preventive control circuit, which eliminates the aforesaid problems. It is therefore the main object of the present invention to provide a hot air-blower off-state residual heat preventive control circuit, which enables the temperature of the hot air-blower to be quickly reduced to the safety range after each use. It is another object of the present invention to provide a hot air-blower off-state residual heat preventive control circuit, which prolongs the service life of the hot air-blower. According to the present invention, a microprocessor is controlled by a power frequency detection circuit to keep the fan motor operating for a predetermined length of time after power supply has been cut off from the main thermal resistor, enabling the temperature of the hot air-blower to be quickly reduced to the safety range within a short time.